Natural rubber has characteristic properties such as large elongation, high elasticity, high tensile strength and tear strength, and satisfactory coating film strength. Thus, natural rubber is utilized in a wide variety of products including household products such as gloves, gloves for surgery, medical devices such as various catheters, nursing devices, and contraceptives. However, there is a report that the gloves for surgery, the medical devices such as the catheters formed of the natural rubber may cause immediate-type (type-I) allergy such as respiratory distress and anaphylactoid symptoms (e.g., angioedema, urticaria, and cyanosis). It is explained that such immediate-type allergy is induced by proteins serving as an antigen contained in natural rubber.
As a method of removing the proteins in natural rubber, there is proposed a method comprising adding a protease such as an alkaline protease and a surfactant to natural rubber latex to carry out protein decomposition treatment, and washing the latex by centrifugation treatment or the like (see Patent Literature 1).
Further, as a method of removing an allergenic proteins which is hardly removed even by such treatment, there is proposed a method comprising adding an alkaline protease to natural rubber latex to carry out protein decomposition treatment, adding a protease having an exopeptidase activity to carry out protein decomposition treatment, and subjecting the proteins and a decomposition product thereof to removal treatment (see Patent Literature 2).
Meanwhile, the inventors of the present invention have proposed, as a method by which protein removal treatment can be carried out in an extremely short period of time, a protein removal treatment method comprising adding a urea derivatives and a surfactant to natural rubber latex to carry out protein denaturation treatment (see Patent Literatures 3 and 4).